U.S. patent application number 10/079660 was filed with the patent office on 2002-08-29 for control method.
Invention is credited to Fallahi, Abdolreza, Sykes, Martin A. P..
Application Number | 20020117152 10/079660 |
Document ID | / |
Family ID | 9909167 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020117152 |
Kind Code |
A1 |
Fallahi, Abdolreza ; et
al. |
August 29, 2002 |
Control method
Abstract
A control method for controlling the timing of fuel injection in
a fuelling system for an engine comprising a fuel injector supplied
with fuel from a source of fuel at high pressure, comprises varying
a drive current which is supplied to the fuel injector at a first
time so as to initiate or terminate a primary injection of fuel and
monitoring the pressure of fuel within the source so as to detect
when a variation in fuel pressure occurs. A time delay is measured,
which represents the difference in time between the first time and
a second, later time at which a variation in fuel pressure within
the source is detected. The measured time delay is used to adjust
the time at which the drive current is varied so as to initiate or
terminate a subsequent injection of fuel, thereby to ensure
initiation or termination of the subsequent injection of fuel
occurs at a required time.
Inventors: |
Fallahi, Abdolreza; (Pinner,
GB) ; Sykes, Martin A. P.; (Gillingham, GB) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS, P.C.
THE PINEHURST OFFICE CENTER, SUITE #101
39400 WOODWARD AVENUE
BLOOMFIELD HILLS
MI
48304-5151
US
|
Family ID: |
9909167 |
Appl. No.: |
10/079660 |
Filed: |
February 20, 2002 |
Current U.S.
Class: |
123/490 ;
123/456 |
Current CPC
Class: |
F02D 2200/0602 20130101;
F02D 41/3836 20130101; F02D 41/402 20130101; F02D 2041/2055
20130101; F02B 3/06 20130101; F02D 41/20 20130101; Y02T 10/44
20130101; Y02T 10/40 20130101 |
Class at
Publication: |
123/490 ;
123/456 |
International
Class: |
F02M 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2001 |
GB |
0104215.9 |
Claims
What is claimed is:
1. A method of controlling the timing of fuel injection in a
fuelling system for a diesel engine fuel system including a fuel
injector supplied with fuel from a source of fuel arranged to
supply fuel to the injector over a range of pressures within a high
pressure fuel range, the method comprising: varying a drive current
which is supplied to the fuel injector at a first time so as to
initiate or terminate a primary injection of fuel; monitoring the
pressure of fuel within the source so as to detect when a variation
in fuel pressure occurs; calculating a time delay between the first
time and a second, later time at which a variation in fuel pressure
within the source is detected, and using the measured time delay to
adjust the time at which the drive current is varied so as to
initiate or terminate a subsequent injection of fuel, thereby to
ensure initiation or termination of the subsequent injection of
fuel occurs at a required time.
2. A method as claimed in claim 1, including: generating a pressure
output signal representative of fuel pressure within the source;
and, filtering noise frequency components from the pressure output
signal and generating a filtered pressure output signal.
3. A method as claimed in claim 2, comprising increasing the drive
current supplied to the fuel injector so as to initiate fuel
injection.
4. A method as claimed in claim 3, comprising determining a rate of
change of the filtered pressure output signal and comparing said
rate of change with a predetermined rate of change indicative of
commencement of injection for a given operating pressure.
5. A method as claimed in claim 2, comprising: measuring an
injection-start delay between (i) the time at which the increase in
the drive current is supplied to the fuel injector so as to
initiate injection and (ii) the time at which the rate of change of
the filtered rail pressure output signal exceeds the predetermined
rate of change of pressure; and using the measured injection
start-delay to adjust the time at which the drive current supplied
to the fuel injector is increased to initiate the subsequent
injection of fuel.
6. A method as claimed in claim 5, comprising: estimating an
injection-start delay for the primary injection of fuel;
calculating the difference between the measured injection-start
delay and the estimated injection-start delay; and, using the
difference to adjust the time at which the drive current is
increased to initiate the subsequent injection of fuel.
7. A method as claimed in claim 1 comprising varying the drive
current by decreasing the current supplied to the fuel injector so
as to terminate fuel injection.
8. A method as claimed in claim 7, comprising determining a rate of
change of the filtered pressure output signal and comparing said
rate of change with a predetermined rate of change indicative of
termination of injection for a given operating pressure.
9. A method as claimed in claim 8, comprising: measuring an
injection-end delay between (i) the time at which a decrease in the
drive current is supplied to the fuel injector so as to terminate
injection and (ii) the time at which the rate of change of the
filtered rail pressure output signal exceeds the predetermined rate
of change of pressure; and, using the measured injection end-delay
to adjust the time at which the drive current supplied to the fuel
injector is decreased to terminate a subsequent injection of
fuel.
10. A method as claimed in claim 9, comprising: estimating an
injection-end delay for the primary injection of fuel; calculating
the difference between the measured injection-end delay and the
estimated injection-end delay; and, using the difference to adjust
the time at which the drive current is decreased to terminate the
subsequent injection of fuel.
11. A method as claimed in claim 1, wherein the subsequent
injection of fuel immediately follows the primary injection of fuel
in an injection cycle.
12. A method as claimed in claim 1, wherein the source of fuel at
high pressure takes the form of a common rail.
13. A method as claimed in claim 4, whereby the step of comparing
said rate of change of the filtered pressure output signal with the
predetermined rate of change is performed in software by reference
to a data map.
14. A method as claimed in claim 8, whereby the step of comprising
said rate of change of the filtered pressure output signal with the
predetermined rate of change is performed in software by reference
to a data map.
15. A method as claimed in claim 2, comprising varying the drive
current by decreasing the current supplied to the injector so as to
terminate fuel injection.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method of controlling fuel
injection in a fuelling system for a diesel engine. In particular,
the invention relates to a method of controlling fuel injection in
a common rail diesel system comprising a common rail arranged to
deliver fuel to a plurality of fuel injectors.
BACKGROUND OF THE INVENTION
[0002] In conventional common rail fuel systems for diesel engines,
it is known to supply a drive current to a fuel injector in order
to cause movement of a valve needle away from a valve seating to
initiate fuel injection. There is a time delay, referred to as the
`injection-start delay`, between the drive current being supplied
to the injector and the commencement of movement of the valve
needle away from the seating. The injection-start delay is
calibrated on test equipment and can be used in an appropriate
control algorithm to ensure fuel injection is initiated at the
desired stage of the injection cycle.
[0003] A problem with this method is that the delay between the
supply of the drive current to the injector and the initiation of
injection can vary depending on, for example, the pressure of fuel
within the common rail, the engine battery voltage and the
temperature of fuel. This can have an adverse effect on engine
performance.
[0004] It is an object of the present invention to provide a
control method for a diesel engine fuel system which alleviates
this problem.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0005] According to the present invention, a method of controlling
the timing of fuel injection in a diesel engine fuel system
including a fuel injector supplied with fuel from a high pressure
fuel source, comprises the steps of;
[0006] varying a drive current which is supplied to the fuel
injector at a first time so as to initiate or terminate a first
injection of fuel,
[0007] monitoring the pressure of fuel within the source so as to
detect when a change in fuel pressure occurs,
[0008] calculating a time delay between the first time and a
second, later time at which a change in fuel pressure within the
source is detected, and
[0009] using the measured time delay to adjust the time at which
the drive current is varied so as to initiate or terminate a
subsequent injection of fuel, thereby to ensure initiation or
termination of the subsequent injection of fuel occurs at a
required time.
[0010] By using the time delay measured for a previous injection of
fuel to adjust the timing of initiation or termination of injection
for a subsequent injection of fuel, any variation in the time delay
due to different operating parameters of the engine can be
compensated for. For example, the method permits variations in the
temperature of fuel, the pressure of fuel within the source, engine
battery voltage and injector manufacturing tolerances to be
compensated for. This improves injection timing and, hence, engine
performance throughout the injector service life.
[0011] In one embodiment, the method includes the steps of:
[0012] generating a pressure output signal representative of fuel
pressure within the source, and
[0013] filtering noise frequency components from the pressure
output signal and generating a filtered pressure output signal.
[0014] The method may comprise the step of increasing the drive
current supplied to the fuel injector so as to initiate fuel
injection.
[0015] In this embodiment, the method may include the step of
determining a rate of change of the filtered pressure output signal
and comparing said rate of change with a predetermined rate of
change of pressure which is indicative of commencement of injection
for a given source pressure.
[0016] In this embodiment of the invention, the method may comprise
the steps of
[0017] measuring an injection-start delay between (i) the time at
which an increase in the drive current is supplied to the injector
so as to initiate injection and (ii) the time at which the rate of
change of the filtered rail pressure output signal exceeds the
predetermined rate of change of pressure,
[0018] and using the measured injection start-delay to adjust the
time at which the drive current supplied to the injector is
increased to initiate the subsequent injection of fuel.
[0019] As the valve needle of the injector commences movement away
from its seating to commence injection, the pressure of fuel within
the source will decrease. The occurrence of this decrease in fuel
pressure can be detected by comparing the rate of change of the
filtered pressure output signal with a predetermined rate of change
of pressure upon commencement of injection (for a given source
pressure) and this is used to provide an indication of the time at
which fuel injection is actually commenced following supply of the
drive current.
[0020] The method may include the steps of estimating an
injection-start delay for the primary injection of fuel,
calculating the difference between the measured injection-start
delay and the estimated injection-start delay and using the
difference to adjust the time at which the drive current is
increased to initiate the subsequent injection of fuel.
[0021] Alternatively, the method may include the step of varying
the drive current by decreasing the current supplied to the
injector so as to terminate fuel injection.
[0022] In one embodiment, the method may include the step of
determining a rate of change of the filtered pressure output signal
and comparing said rate of change with a predetermined rate of
change indicative of termination of injection for a given source
pressure.
[0023] Conveniently, the method may include the steps of:
[0024] measuring an injection-end delay between (i) the time at
which decrease in the drive current is supplied to the injector so
as to terminate injection and (ii) the time at which the rate of
change of the filtered rail pressure output signal exceeds the
predetermined rate of change of pressure,
[0025] and using the measured injection end-delay to adjust the
time at which the drive current supplied to the injector is
decreased to terminate a subsequent injection of fuel.
[0026] The method may comprise the step of estimating an
injection-end delay for the primary injection of fuel, calculating
the difference between the measured injection-end delay and the
estimated injection-end delay and using the difference to adjust
the time at which the drive current is decreased to terminate the
subsequent injection of fuel.
[0027] The subsequent injection of fuel may immediately follow the
primary injection of fuel in an injection cycle.
[0028] The method is particularly suitable for use in controlling
the injection of fuel in a common rail fuel system comprising a
common rail for delivering fuel to a plurality of fuel
injectors.
[0029] As the source pressure in a diesel engine fuel system is
variable, it is necessary to compare the rate of change of the
filtered pressure output signal with a predetermined rate of change
of pressure for any given source pressure.
[0030] Thus, conveniently, the step of comparing said rate of
change with a predetermined rate of change is performed in software
by reference to a data map or look-up table.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Other advantages of the present invention will be readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying, by way of example only, with reference to
the accompanying FIGURE which illustrates various operating
parameters of a fuel system as a function of time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] It is known to control the injection of fuel from a fuel
injector by supplying a drive current to an actuator arrangement
forming part of the injector so as to control movement of a fuel
injector valve needle. Typically, for example, the actuator
arrangement may take the form of a piezoelectric actuator
arrangement, including one or more piezoelectric elements, or an
electromagnetic actuator arrangement including an energisable
winding. By supplying a drive current to the actuator arrangement,
movement of the valve needle away from a valve seating is
controlled, either directly by the actuator arrangement or through
a hydraulic link to the actuator arrangement, so as to permit fuel
injection through one or more outlet openings associated with the
injector.
[0033] Referring to the accompanying FIGURE, Trace A represents a
typical drive current which may be supplied to the injector to
initiate movement of the valve needle away from its seating. The
supply of the drive current is controlled by appropriate
programming of an Engine Control Unit (ECU) or Engine Management
System (EMS) in a manner which would be familiar to a person
skilled in the art of engine control systems. Trace B represents
movement of the valve needle away from the seating, such movement
being initiated at time T.sub.2. It can be seen from Traces A and B
that the time, T.sub.2, at which valve needle movement away from
the seating is initiated, and hence the time at which fuel
injection is commenced, occurs later than the time, T.sub.1, at
which the drive current is supplied to the injector. The time
difference, .DELTA.T, represents the delay in time between the
drive current being supplied to the injector and the injection of
fuel being initiated. For the purpose of this specification, the
time difference, .DELTA.T, shall be referred to as the
`injection-start delay`.
[0034] The source of fuel delivering fuel to the injectors may take
the form of a common rail charged with fuel at high pressure by
means of a high pressure fuel pump. The pressure of fuel within the
common rail is conveniently measured by means of a rail pressure
sensor, the output from which is represented by Trace C.
[0035] In order to utilise the rail pressure output signal in the
control method of the present invention, it is necessary to apply a
signal processing technique to remove noise frequency components
(visible in Trace C). For example, a mathematical filtering process
may be applied to the rail pressure output signal using an
appropriate transfer function to remove such unwanted frequency
components, thereby generating a filtered rail pressure output
signal (Trace D). It can be seen from Trace D that the resultant,
filtered rail pressure output signal is substantially free of
noise.
[0036] When it is desired to inject fuel, the drive current (Trace
A) is supplied to the injector to initiate movement of the valve
needle away from its seating. Upon commencement of fuel injection,
fuel is injected into an engine cylinder or other combustion space
through the fuel injector outlet opening(s), giving rise to a
measurable reduction in fuel pressure within the common rail. It
can be seen in the accompanying figure that the processed rail
pressure signal (Trace D) decreases at time, T.sub.2, when
injection of fuel through the outlet opening is initiated.
[0037] It has been found that the injection-start delay, .DELTA.T,
between the application of the drive current to the actuator
arrangement and initiation of movement of the valve needle to
commence injection varies depending on the operating parameters of
the engine, such as, for example, the pressure of fuel within the
common rail prior to injection, the engine battery voltage and the
temperature of fuel within the common rail. In order to compensate
for such variations in the injection-start delay, an adjustment is
made to the timing of the application of a subsequent drive
current, based on the preceding drive current, so as to ensure
injection is initiated at the required time.
[0038] Initially, an estimated injection-start delay,
.DELTA.T.sub.EST, between the supply of the drive current to the
injector and the commencement of fuel injection is used to initiate
a primary injection of fuel at approximately the required time. The
output signal from the rail pressure sensor (Trace D) is then used
to determine the time at which fuel injection is actually
commenced.
[0039] In order to determine the time at which fuel injection is
actually commenced, the rate of change of pressure is determined
from the filtered rail pressure output signal (Trace D). It is
necessary to measure the rate of change of the filtered rail
pressure output signal, as opposed to the directly measured rail
pressure output signal (Trace C), otherwise the effects of noise on
the direct signal may give rise to spurious results. For injection
at a given rail pressure, the measured rate of change of pressure
is compared with pre-calibrated data indicative of the rate of
change of pressure upon commencement of injection. Conveniently,
this may be achieved in software through use of data maps or
look-up tables. If the rate of change of the filtered pressure
output signal exceeds the predetermined rate of change of pressure
(for the particular rail pressure), the time, T.sub.2, is recorded.
By measuring the time, T.sub.2, at which fuel pressure within the
common rail is decreased, an actual injection-start delay,
.DELTA.T.sub.ACTUAL, between the supply of the drive current to the
injector and the commencement of fuel injection is then
calculated.
[0040] The actual injection-start delay, .DELTA.T.sub.ACTUAL, is
then compared with the estimated injection-start delay,
.DELTA.T.sub.EST, to determine an offset which is used to adjust
the time, T.sub.1, at which the drive current is supplied to the
injector for the subsequent injection event so as to ensure fuel
injection is commenced at the required time.
[0041] It will be appreciated that, as the diesel fuel injection
system is operable over a range of rail pressures, the step of
comparing the measured rate of change of the filtered pressure
output signal with the pre-determined rate of change of pressure
will depend on the rail pressure and it is therefore necessary to
pre-calibrate the system over the range of pressures at which the
fuel system will operate.
[0042] A suitable adjustment can also be made for further,
subsequent injections based on a preceding injection event. It will
be appreciated that, in order to reduce processing time, an
adjustment to drive current supply timing need not be made for
every injection event, but may be made for selected injection
events, for example every tenth injection of fuel in an injection
cycle.
[0043] It will be appreciated that the method of the present
invention is not limited to use in controlling the time at which
fuel injection commences, but may be used to control the timing of
termination of injection. Upon closing movement of the valve needle
against its seating to close the outlet opening, the pressure of
fuel within the common rail will be increased. In this case, it is
necessary compare the rate of change of the filtered pressure
output signal with a pre-determined rate of change in pressure (for
a given source pressure) which is indicative of termination of
injection when the valve needle is seated. An injection-end delay
is then calculated as the time difference between the time at which
the drive current is removed from the injector and the rate of
change in the filtered pressure output signal exceeding said
predetermined rate of change in pressure. The difference, or
offset, between an estimated injection-end delay and an actual
injection-end delay is then calculated and is used to adjust the
time at which the drive current is removed from the injector to
terminate a subsequent injection event.
[0044] A suitable adjustment can also be made for further
subsequent injections based on a preceding injection event.
[0045] The invention provides the advantage that the timing of
initiation or termination of injection can be adjusted throughout
the service life of the injector, thereby improving engine
performance. A wide range of manufacturing tolerances can be
compensated for using the aforementioned technique, and an improved
engine performance can be maintained over a range of engine
operating conditions.
[0046] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. The
invention may be practiced otherwise than as specifically described
within the scope of the appended claims.
* * * * *